1x MythicPlusDrop/module/Schedule.lua:167: attempt to index local 'affix' (a nil value)
[string "@MythicPlusDrop/module/Schedule.lua"]:167: in function <MythicPlusDrop/module/Schedule.lua:134>
[string "=[C]"]: in function `Update'
[string "@Blizzard_ChallengesUI/Blizzard_ChallengesUI.lua"]:116: in function <...dOns/Blizzard_ChallengesUI/Blizzard_ChallengesUI.lua:107>

Locals:
weeklyChest = Frame {
Highlight = Texture {
}

Ok I'll upload the version to curseforge tomorrow, but without debug output. Thx for testing the files.

I tried both and for now no lua error appears.
Neither does the debug line you added

I have no gametime at this moment, can you test this version pls:
MythicPlusDrop.zip

Here is a other version for testing:
MythicPlusDrop.zip